Electronic communication switches have unpredictable power requirements, due in part to the widely varying and unpredictable communication loads and Power over Ethernet (PoE) loads they are called upon to handle. This, in combination with a movement towards energy efficiency, is creating a need for new methods for managing power in network switches.
A variety of existing techniques are used to manage power in network switches. For example, in modular switches, which consist of a set of switching modules operating in cooperation with each other, the power supplied to each of the switching modules is managed to assure that: (1) the total power supplied to the switching modules is not greater than the capacity of the installed power supplies; and (2) to maintain enough power head room to handle a power supply going down without affecting the switching modules' operation. As another example, switch ASIC vendors offer switching ASICs that can power down portions of the switching circuitry to save power.
As yet another example, stackable switches have PoE power management, which enables the switch to provide power to connected devices over Ethernet connections. Such switches do not, however, have the ability to dynamically re-allocate power between internal switch circuitry and power provided to external devices via PoE.
There is a catch-22 problem managing power allocation between switch port operation and PoE power delivery. If one were to first measure the power used by the switching circuitry to estimate the amount of power the circuitry will need, the estimate will be low because the circuitry is in an idle state and therefore not consuming as much power as when it is passing data in an active state. If one were then to allocate PoE power based on this low estimate and then turn on the external devices, the devices would begin to transmit data, thereby activating the switching circuitry, which would not receive sufficient power. On the other hand, if one first tries to allocate all the PoE power requested, insufficient power may be reserved for the switching circuitry. To avoid such problems, existing switches typically supply the maximum (worst-case) power to the switching circuitry and to PoE at all times.